Tank construction

ABSTRACT

An improved upstanding cylindrical tank is provided, in one aspect of the invention, with a ring-like stiffening member at its open upper end to resist flexure and deformation of the side wall structure under wind loading. The stiffening member has a cylindrical inner flange portion formed integrally with the tank wall, an annular web portion extending radially outward from an upper part of the upper flange portion, and a cylindrical outer flange portion depending from an outer part of the web portion and arranged concentrically with the inner flange portion. The stiffening member has a minimum vertical moment of inertia and is configured to have its vertical neutral axis located approximately midway between the furthermost fibers of the inner and outer flange portions. A tank is provided, in another aspect of the invention, with means for resisting an overturning moment which produces additional tensile forces in a leading portion of the wall structure and additional compressive forces in a trailing portion thereof. The resisting means are arranged near the bottom of the tank and include vertically-spaced upper and lower annular flanges extending radially outwardly from the side wall structure, and a plurality of circularly-spaced anchor bolts arranged to act on the upper flange to resist the additional tensile forces. The centroid of the polar moment of inertia of the resisting means is located equidistant from the furthermost fibers of the upper and lower flanges.

United States Patent Rossitto et al.

Nov. 4, 1975 TANK CONSTRUCTION [75] Inventors: Vincent J. Rossitto,Buffalo; Robert E. Baker, North Evans; James J. Jarvis; James N. DeSerio, both of Kenmore, all of NY.

[73] Assignee: Metal-Cladding, Inc., North Tonawanda, NY.

[22] Filed: Mar. 6, 1974 [21] Appl. No.: 448,669

[52] US. Cl. 220/18; 220/9 LG [51] Int. Cl. B65D 25/24 [58] Field ofSearch 220/18, 1 B, 73, 74, 5, 220/69, 70, 9 LG [56] References CitedUNITED STATES PATENTS 929,446 7/1909 Keiner 220/70 1,972,807 9/1934Waters 220/1 B 3,025,992 3/1962 Humphrey 220/5 3,275,181 9/1966 Leclou220/18 3,448,886 6/1969 Todd et al. 220/18 X 3,460,705 8/1969 Green220/1 B X Primary ExaminerDonald F. Norton Assistant Examiner-Steven M.Pollard Attorney, Agent, or Firm-Sommer & Somrner in one aspect of theinvention, with a ring-like stiffening member at its open upper end toresist flexure and deformation of the side wall structure under windloading. The stiffening member has a cylindrical inner flange portionformed integrally with the tank wall, an annular web portion extendingradially outward from an upper part of the upper flange portion, and acylindrical outer flange portion depending from an outer part of the webportion and arranged concentrically with the inner flange portion. Thestiffening member has a minimum vertical moment of inertia and isconfigured to have its vertical neutral axis located approximatelymidway between the furthermost fibers of the inner and outer flangeportions.

A tank is provided, in another aspect of the invention, with means forresisting an overturning moment which produces additional tensile forcesin a leading portion of the wall structure and additional compressiveforces in a trailing portion thereof. The resistingmeans are arrangednear the bottom of the tank and include vertically-spaced upper andlower annular flanges extending radially outwardly from the side wallstructure, and aplurality of circularly-spaced anchor bolts arranged toact on the upper flange to resist the additional tensile forces. Thecentroid of the polar moment of inertia of the resisting means islocated equidistant from the furthermost fibers of the upper and lowerflanges.

4 Claims, 19 Drawing Figures US. Patent Nov. 4, 1975 Sheet 1 of43,917,104

US. Patent Nov. 4, 1975 Sheet 2 of4 3,917,104

US. Patent Nov. 4, 1975 Sheet 3 of4 3,917,104

GROUND MOTION COMPRESSION TENSION CMAX US. Patent Nov. 4, 1975 Sheet4of4 3,917,104

TENSION SIDE COMPRESSION SIDE TANK CONSTRUCTION BACKGROUND OF THEINVENTION The present invention relates to improvements in tankconstructions, particularly in upstanding open-top cable-wrappedfiberglass reinforced plastic tanks of the type disclosed in US. Pat.No. 3,025,992 which are especially suited to contain or store corrosiveliquids.

This form of tank construction includes a cylindrical wall structurewhich may be formed and transported sectionally and thereafter assembledin situ. A steel cable is helically wrapped around the tank such thatthe vertical spacing between adjacent cable convolutions is closer nearthe bottom of the tank than at the top. Since this external cableoperatively resists the hoop stress exerted on the tank wall by theliquid contained within the tank, the sectional wall structure may bemanufactured to have an economically thin radial thickness. i

However, as the wall structure is relatively thin in comparison to thetank diameter and height, the wall structure of the assembled tank isrelatively flexible, particularly at its open upper end, and may deformor flex under normal wind loading when the tank is empty.

Moreover, such a tank, and other types of tank constructions, may haveto be designed to resist seismic forces and wind forces which apply anoverturning moment to the tank. Under application of such seismicforces, liquids within the tank may exert a hydrodynamic impulse on thewall structure, producing a tensile force in one portion thereof and acompressive force in another portion thereof.

SUMMARY OF THE INVENTION The present invention, in one aspect, relatesto improvements in upstanding thin-walled fiberglass reinforced plastic(FRP) tanks, adapted to contain or store a liquid or fluid material andhaving an annular side wall structure terminating in an annular rim atits open upper end, and wherein a portion of such structure isconfigured as a cylindrical segment having an upper arcuate end forminga part of the rim.

The invention provides a stiffening member located at the upper end ofthe segmented portion for increasing the flexure resistance thereofproximate the rim. The stiffening member includes an inner flangeportion configured as a cylindrical segment and secured to the segmentedportion and extending upwardly therefrom; a web portion formedintegrally with and extending radially outward from an upper part of theinner flange portion; and an outer flange portion configured as acylindrical segment formed integrally with and depending from an outerpart of the web portion and arranged generally concentric with andspaced radially from the inner flange portion.

Preferably, the inner flange portion is formed integrally with thesegmented portion and has a vertical height of at least sixteen timesits radial thickness. The web portion may have a vertical thicknessequal to the radial thickness of the inner flange portion, and a radialextent of one-twentieth of the inner radius of the segmented portion.The radial thickness of the outer flange portion is desirably twice theradial thickness of the inner flange portion.

- The minimum value of the vertical moment of inertia is computable as afunction of the anticipated wind load, the outer diameter of the sidewall structure, and

Youngs modulus for FRP. After the minimum moment of inertia has beencomputed, the vertical height of the outer flange portion may bedimensioned to locate the neutral axis of the vertical moment of inertiaapproximately midway between the furthermost fibers of the inner andouter flange portions.

The present invention, in a second aspect, provides resisting means atthe lower portion of a tank for withstanding an overturning momentapplied thereto, such moment producing tensile forces in a leadingportion of the wall structure and compressive forces in a trailingportionthereof. I

The resisting means includes annular lower flange means extendingoutwardly from the tank and having a lower face arranged in downwardlythrusting relation to a support, annular upper flange means extendingoutwardly from the tank and arranged in vertically spaced relation tothe lower flange means, and anchorage means secured to the support andarranged to exert a downward force on the upper flange means. The lowerface of the lower flange means is arranged to resist the compressiveforce in the trailing portion of the wall structure.

The anchorage means includes a plurality of circularly spaced bolt meansarranged to act on the upper surface of the upper flange means throughan intermediate contact plate. In one embodiment, the bolt meansincludes a plurality of anchor bolts having their lower ends suitablyembedded in the support, and a corresponding plurality of nuts threadedonto the upper ends of each of the anchor bolts and arranged to act onthe upper surface of the plate. The anchorage means cooperates with theupper flange means to resist the additional tensile forces produced inthe leading part of the wall structure.

The resisting means is configured to locate the centroid of its polarmoment of inertia approximately equidistant from the furthermost fibersof the upper and lower flange means.

Accordingly, one object of the present invention is to provide astiffening member to resist deformation of the upper rim of an open-top,relatively flexible, upstanding tank under application of wind loads.

Another object is to provide an improved tank capable of withstandingapplication of an overturning moment which produces tensile forces in aleading portion of the side wall structure and compressive forces in atrailing portion thereof.

These and other objects and advantages will become apparent from theforegoing and ongoing specification which includes the drawings and theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of anempty, upstanding, open-top, thin-walled cylindrical, fiberglassreinforced plastic tank to which a uniformly distributed unidirectionalwind load is about to be applied.

FIG. 2 is a perspective schematic view of the tank depicted in FIG. 1after application of the wind load and particularly illustrating thenature of the deformation of the annular side wall structure and furtherillustrating a schematic flow gradient about the upper rim of thedeformed tank.

FIG. 3 is an isolated top plan view of the deformed rim shown in FIG. 2,depicting the extent of such rim deformation from its original circularshape, such original undeformed shape being shown in phantom.

FIG. 4 is a perspective view of an improved empty, upstanding, open-top,thin-walled, cylindrical fiberglass reinforced plastic tank, generallysimilar to the tank depicted in FIG. 1 but additionally provided withthe inventive stiffening member.

FIG. 5 is an enlarged top plan view of the improved tank, taken on line5-5 of FIG. 4, and particularly showing the annular'web portion of thestiffening member.

FIG. 6 is an enlarged fragmentary vertical sectional view of the upperportion of the cylindrical wall structure of the tank, taken on line 6-6of FIG. 4, such view illustrating the stiffening member incross-section.

FIG. 7 is a perspective view of an alternative type of tankconstruction, particularly suited for large capacity tanks, wherein theside wall structure is formed by assembling a plurality of cylindricalsegments, each of the upper segments being shown as including theinventive stiffening member.

FIG. 8 is an enlarged perspective view of the outside of one of theupper cylindrical segments shown in FIG. 7 and particularly illustratingthe configuration of such segment and the inventive stiffening memberformed integrally therewith, and also depicting the relation of suchsegment to adjacent segments of similar construction illustrated inphantom.

FIG. 9 is an enlarged fragmentary vertical sectional view of an upperpart of the upper segment depicted in FIG. 8 and showing thecross-section of the stiffening member, this view being taken on line 99of'FIG. 8.

FIG. 10 is an enlarged fragmentary perspective view of the joint betweentwo adjacent upper segments and showing the placement of battens on theadjacent stiffening members.

FIG. 11 is a perspective view of the tank depicted in FIG. 1 showncontaining a liquid and to which a horizontal distributed trapezoidalseismic load is about to be applied.

FIG. 12 is an exaggerated schematic representation of a side elevationof the tank after application of the seismic load depicted in FIG. 11and having a portion of the wall structure broken away to illustrate theliquid exerting a dynamic impulse on the wall structure, such impulseplacing the leading or right portion of the wall structure in tensionand the trailing or left portion thereof in compression.

FIG. 13 is a perspective schematic view of a lower part of the wallstructure depicted in FIG. 12, showing the point of maximum tension inthe leading or right portion, and the point of maximum compression inthe trailing or left portion.

FIG. 14 is a perspective schematic view of the rotational momentsproduced in the wall structure due to the tensile and compressive forcesdepicted in FIG. 13.

FIG. 15 is a perspective view of an improved tank, generally similar tothe tank depicted in FIG. 11, but provided with the inventive resistingmeans.

FIG. 16 is an enlarged fragmentary perspective view of a portion of theresisting means illustrated in FIG. 15, this view particularlyillustrating the upper and lower flange means and the anchorage means.

FIG. 17 is a fragmentary vertical sectional view of the lower portion ofthe tank. taken on line l7I7 of FIG. 16, and showing the resisting meansin cross-section.

FIG. 18 is a schematic fragmentary vertical sectional view of theresisting means at the point of maximum compression and depicting theforces acting therein.

FIG. 19 is a schematic fragmentary vertical sectional view of theresisting means at the point of maximum tension and depicting the forcesacting therein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS STIFFENING MEMBER (FIGS. l-10)Referring to FIG. 1, an empty upstanding open-top tank, generallyindicated at 10, is depicted as including an annular side wall structure11 having an annular rim 12 at its open upper end, and a horizontalcircular bottom resting on a lower supporting foundation 13. The sidewall structure 11 is specifically illustrated as being a thin-walledvertical cylinder having an inner cylindrical surface 14 and an outercylindrical surface l5 spaced radially therefrom by the thickness (t) ofthe wall structure. A marginal portion 16 of the bottom is shownextending radially beyond the outer surface 15 of the side wallstructure. A plurality of circularly spaced bolts l8 are suitablyanchored in the foundation and are arranged to act on the upper surfaceof marginal portion 16 to secure the tank to the foundation.

Tank '10 is formed of a fiberglass reinforced plastic (FRP) materialtoprovide a high degree of corrosion resistance to various liquids andfluid materials which may be stored therein. In cross-section, such FRPma-' of FRP is relatively low, being in the order of 1.0 X 10 psi intension and 1.25 X 10 psi in compression, the

side wall structurell of the tank must be further strengthened to resistthe hoop stress exerted by a height of stored liquid acting on the innersurface 14 of the tank. To this end, a steel cable having a greatermodulus of elasticity, typically on the order of 21 X 10 psi, has itslower end suitably anchored (not shown) proximate the bottom of thetank, its intermediate portion helically wound around the outer surface15 of the tank such thatthe vertical spacing between adjacent cableconvolutions 19 increases with height'above the tank bottom, and itsupper end suitably secured (not shown) proximate the upper end of thetank. Additional features and details of this known form of cablewrappedFRP tank construction may be found in US.

Pat. No. 3,025,992, the disclosure of which is hereby incorporated byreference. Large volume storage tanks have been constructed according tothe teaching of this patent and, for a cylindrical tank having an innerdiameter of 20 feet and a height of 27 feet, a typical economicthickness of the side wall structure might be about A inch. Thehelically wound cable is wrapped loosely around the outer surface of thetank andis designed solely to resistthe hoop stress exerted by theservice fluid on the wall structure. However, when empty and subjectedto wind loads, such tanks are known to experience significantdeformation, especially about their open upper ends. Moreover, the sidewall structure 11 must be capable of withstanding repeated stressreversals as the direction of the wind changes.

When an assumed unidirectional distributed wind load having a magnitudeof w lbs/ft as schematically represented in FIG. 1, is applied to thetank, the flow gradient of such wind load around the tank causes theside wall structure 11 to flex or deform to the general shapeillustrated in FIG. 2. Since the bottom of the tank is fixed to thefoundation by the plurality of anchor bolts 18 acting on flange 16, thecircular crosssectional shape of a lower portion of the side wallstructure proximate flange 16 will be maintained. However, the upper rim12 of the wall structure is unsupported and unrestrained and may distortfrom its substantially circular shape to the shape of a heart pointingin the leeward direction, as best illustrated in FIG. 3. A staticpressure will be applied at the center 19 of the windward side of therim, causing it to bend sharply inward. The force of such load may causethe lateral portions 20, 21 of the rim to bulge outwardly in a directiongenerally transverse to the direction of the wind. At the same time, alow pressure region may develop on the leeward side of the rim, urging acentral portion 22 thereof to flex sharply outwardly. The intermediateportion of the side wall structure 11 is depicted as being in generallysmooth, continuous transition from its restrained circular cross-sectionproximate the bottom to its heartshaped cross-section at the upper rim,as best shown in FIG. 2. Maximum stress will occur at points 19, 22 ofsharp, discontinuous flexure on the windward and leeward sides of therim, respectively.

While it is convenient to visualize the wind load as beingunidirectional and uniformly distributed, in reality, its direction andmagnitude are continuously varying. Hence, the upper rim 12 of the tank,being the section of maximum distortion, is subjected to repeated stressreversals which greatly reduce the fatigue life of the tank. Unlike acylindrical tank of steel or concrete, the wall structure of a largecapacity FRP tank is relatively flexible because its radial thickness istypically small with respect to the diameter and height of the tank. Ithas been observed that the upper rim of an FRP tank may actually quiveror vibrate under normally encountered wind loading, further decreasingthe fatigue life of the tank especially at the points of maximum stressconcentration in the rim.

In FIG. 4, the tank depicted in FIG. 1 is shown as being additionallyprovided with the inventive stiffening member 23 to increase theflexural rigidity of its open upper end to resist wind loads. As bestillustrated in FIGS. 4-6, the inventive stiffening member 23 is locatedat the open upper end of the tank and is secured to or formed integrallywith an upper part 24 of'the cylindrical side wall structure 11.

As best shown in FIG. 6, the stiffening member 23 broadly includes aninner flange portion 25, a web portion 26, and an outer flange portion28. The inner flange portion 25 is a thin-walled vertical cylinderhaving an inner cylindrical surface 29, an outer cylindrical surface 30spaced radially therefrom by the thickness (t) of the inner flangeportion, and having an open upper end 31. Preferably, inner flangeportion 25 is formed integrally with the side wall structure, or asegmented portion thereof, so as to constitute an upward continuationthereof having a vertical height at least 16 times the radial thickness(t) of the side wall structure.

The web portion 26 is shown as being a horizontal annular plate formedintegrally with and extending radially outwardly from an upper marginalpart of the inner flange portion proximate the upper end 31 thereof, andas having a vertical thickness equal to the thickness (z) of the sidewall structure and a horizontal upper annular surface 27. Desirably, themaximum radial extent of the web portion is 0.05 of the inner radius(R,) of the tank.

The outer flange portion 28 is a larger diameter vertical cylinderspaced radially from and arranged concentrically with inner flangeportion 25, and formed integrally with and depending from an outermarginal part of the web portion. The outer flange portion 28 has avertical height;(h), an inner cylindrical surface 33 and an outercylindrical surface 34 spaced radially therefrom by the thickness of theouter flange portion, desirably twice the thickness (t) of annular sidewall structure 11.

In a presently preferred embodiment, the stiffening member 23 is formedintegrally with the cylindrical side wall structure 11 such that theinner flange portion constitutes an integral upward continuationthereof. In some applications, it may be desirable to form or assemblethe stiffening member separately from the tank and subsequently secureit to the upper end of the wall structure, as by overlapping the innerflange portion of the stiffening" member on the inside or outside of theside wall structure.

. In FIG. 7, an alternative sectional type of construction, alsodisclosed in US. Pat. No. 3,025,992 and particularly suited for erectingtanks of large height and/or diameter, is shown as including an annularside wall structure 11 formed by assembling a plurality of annularsegments together and about which the convolutions 19 of a helicallywound cable are wrapped. This sectional annular wall structure 11' isshown as being a thin-walled vertical cylinder and formed by assemblingeighteen cylindrically segmented sections into a bottom ring of sixlower segments 35, a middle ring of six intermediate segments 36, and atop ring of six upper segments 38, each of such segments being shown asinscribing an arc of Each intermediate segment 36 is shown as includinga vertical left and right side 39, 40, respectively; a horizontalarcuate top and bottom 41, 42, respectively; and inner and outer arcuatesurfaces 43, 44, respectively, severally occupying the inscribing angleof 60 and separated by the thickness (t) of the segmentJTheseintermediate segments 36 are additionally shown provided with aperipheral mounting flange 45 extending radially outwardly from the top,bottom, and sides thereof, and by which adjacent segments may beheldtogether during assembly of the tank 10.

As best shown in FIGS. 7 and 8, each of upper segments 38 is similarlyconfigured to have left and right vertical sides 39, 40, respectively; ahorizontal arcuate top 41' and bottom 42; and inner and outer arcuatesurfaces 43', 44' also occupying an inscribed angle of 60 and separatedby the radial thickness (t) of the upper segment. However, each of uppersegments 38 is additionally provided with a stiffening member 23' at itstop 41 In FIG. 9, the stiffening member 23' of each upper segment isshown as including an inner flange portion 25', a web portion 26', andan outer flange portion 28, otherwise configured and dimensioned asbefore described.

After the tank shown in FIG. 7 has been assembled, it is necessary toseal the joints between adjacent segments to rigidify the wall structureand to provide a functional liquid-impervious inner surface 14. As bestshown in FIG. 7, a plurality of battens or strips 46 of FRP material maybe positioned over the horizontal and vertical joints between adjacentassembled segments and adhered with a suitable bonding resin to theinner surface 14 of the tank to provide the necessary strength and seal.These battens are also shown applied to join the adjacent su faces 29 ofthe adjacent inner flange portions 25 of adjacent upper segments 38.Additional plate-like battens 48, 49 may be resin bonded to the upperand outer surfaces 27, 34 of the web and outer flange portions 26', 28,respectively, to join these portions of adjacent stiffening members 23'into an operative, circular, ring-like stiffening member, as best shownin FIG. 10.

In either type of described construction, the tank is initially designedto accommodate the intended service fluid and to have the requisiteheight, inner and outer diameters, and radial thickness. Thereafter, thelength of cable and the spacing between adjacent cable convolutions atvarious heights above the bottom may be calculated.

The stiffening member 23 may then be dimensioned, knowing the radialthickness (13) and the inner radius (R) of the wall structure. Innerflange portion 25 is preferably configured to be an upward integralcontinuation of the tank wall structure having a radial thickness (t)and a vertical height of sixteen times this thickness (t). The webportion 26 is dimensioned to have a vertical thickness of (t) and amaximum radial extent, from the inner surface 29 of inner flange portion25 to the outer surface 34 of outer flange portion 28, of (0.05) of theinner radius (R) of the tank. The outer flange portion 28 is selected tohave a greater radial thickness equal to twice the thickness (t) of thewall structure. Hence, only the vertical height (h) of the outer flangeportion remains unknown.

The minimum vertical moment of inertia for the stiffening member may becalculated according to the formula:

where:

l the minimum vertical moment of inertia of a section of the stiffeningmember w the anticipated wind load applied horizontally at the the upperend of the tank per unit of tank vertical height D the outer diameter ofthe wall structure E, Youngs modulus for fiberglass reinforced plasticin compression Knowing the value of ly the vertical height (h) of outerflange portion 28 may be computed to locate the neutral axis (N.A.) ofthe vertical moment of inertia approximately midway between innersurface 29 and outer surface 34 such that the stiffening member will beequally capable of resisting both inward and outward flexure.

It should be clearly understood that the stated preferred dimensions ofthe stiffening member are merely intended to reduce the number ofvariables such that a person having ordinary skill in this art may moreeasily locate the neutral axis of the vertical moment of inertia bysimply varying the vertical height (h) of the outer flange portion, anddo not constitute a limitation on the claims unless expressed therein.

As used in the appended claims, the word segment refers to either adiscrete separate part or an imaginary subdivision of the surface ofrevolution.

BOTTOM RING GIRDER (FIGS. 11-19) Under known design standards, anupstanding cylindrical tank, adapted to contain a liquid or a fluidmaterial, may have to be designed to withstand a minimum horizontalseismic force (F,) which applies an overturning seismic moment (M to thetank. These standards contemplate that the total seismic force (F,) isthe sum of a first horizontal force (F, related to the dead load exertedby the weight of the tank and acting at its centroid (2 above the tankbottom, and a second horizontal force (F, related to the live loadexerted by a dynamic impulse of the liquid exerted on the walls of thetank during a rapid horizontal translation of the bottom of the tank andacting at the centroid (2 of the effective weight of the liquid.Specifically, the

anticipated magnitude of F may be calculated as a function of the totalweight of the tank (W the weight of the contained liquid (W the ratio (kof the dynamic mass of the liquid to its total mass, and a constant (c)characteristic of the seismic conditions at the geographical location ofthe tank, according to the general formula:

The overturning seismic moment (M may then be computed as the sum ofmoment (M produced by the seismic force attributable to the tank (Facting at its centroid (z above the bottom of the tank, and the moment(M produced by the seismic force attributable to the liquid (F acting atits effective centroid (2 above the bottom of the tank. Accordingly,

s s s s 7) x L) It will be appreciated by those skilled in this art thatthe wind load may produce a similar overturning moment on the tank.

In FIG. 11, the tank 10 illustrated in FIG. 1 is shown as containing aliquid and about to be subjected to a distributed trapezoidal load, suchload schematically representing the aggregate lateral seismic force (F,)exerted on the tank during an earthquake. As best shown in FIG. 12, theapplied total seismic force (F,,) includes a uniformly distributedportion attributable to the dead.

load of the tank and having a resultant force (F acting at its centroid(z above the bottom, and a second portion having a generally trapezoidalcross-section attributable to the live load of the liquid and having aresultant force (F, acting at its effective centroid (z above the bottomof the tank.

For purposes of further illustration, a cable-wrapped FRP tank having aninner radius of inches, an outer radius (R of 120.5 inches, filled witha liquid having a specific gravity of 1.70, and geographically locatedin an area where c 0.10, may have to be designed to withstandapplication of seismic forces and moments of the following magnitude: i

F 1053 lbs. (z 13.5)

F, F F, 75,406 lbs.

M (F (z 12,519 ft.-lbs.

M (F, (z,,) 813,050 ft.-lbs.

M =M +m =825,569 ftL-lbs If. under application of the total horizontalseismic force (F the foundation 13 is rapidly translated in a horizontaldirection, the liquid will tend to remain at rest and exert a dynamicimpulse on the trailing or left portion 50 of the side wall structure 11and urge such structure to flex, as best viewed in the exaggeratedschematic representation of FIG. 12. Hence, the liquid will actdynamically under such seismic translation to produce an upward tensileforce in a leading or right portion 51 of the wall structure 11 and adownward compressive force in an opposite trailing or left 50 portionthereof, as may be viewed in the perspective schematic of FIG. 13. Sincethese tensile and compressive forces act in opposite directions and areseparated by the diameter of'the tank (FIGS. 12 and 13), an upwardly andinwardly curling torsional moment (M will be applied to that portion ofthe wall structure which is in tension, and a downwardly and inwardlycurling' torsional moment (M,) will be applied to that portion of thewall structure which is in compression, as schematically depicted inFIG. 14. In the illustrative example given, application of the totalseismic moment (M will produce an additional seismic flexure stress (fl)at the bottom of the side wall structure, calculable according to theequation:

Referring to FIGS. and 16, an improved tank 52, generally similar to thetank depicted in FIGS. 11 and 12, is shown as including an annular sidewall structure 53; a bottom 54 (FIG. 16); and means, generally indicatedat 55, arranged at the lower portion of the tank for resisting theadditional flexure stress produced in the side wall structure bytheapplication of an overturning moment to the tank. In FIGS. 16 and 17,such resisting means 55 is shown as broadly including annular upper andlower flange means 56, 58, respectively, and anchorage means 59.

The annular side wall structure 53 is specifically shown as being anupstanding thin-walled cylinder having an upper cylindrical part 60 anda lower cylindrical part 61. Upper cylindrical part 60 includes an innercylindrical surface 62, a concentric outer cylindrical surface 63 spacedfrom inner surface 62 by the radial thickness (t) of the upper part, andan annular first flange portion 64 extending radially outwardly from itslower end 65. First flange portion 64 has horizontal upper and lowersurfaces 66, 68, respectively, and is preferably formed integrally withupper cylindrical part 60.

Lower cylindrical part 61 similarly includes an inner cylindricalsurface 69 and a concentric outer cylindrical surface 70 spaced frominner surface 69 by the radial thickness (t) of lower part 61; andfurther includes an integral second annular flange portion 71 extendingradially outwardly from its upper end 72, and an integral third annularflange portion 73 extending radially outwardly from its lower end 74.The second annular flange portion 71 has upper and lower annularsurfaces 75, 76, respectively. Similarly, the third flange portion 73has upper and lower annular surfaces 78, 79, respectively. Preferably,the vertical height of lower cylindrical part 61 may be between sixteenand eighteen times its radial thickness (t).

As best shown in FIG. 17, the lower end 65 of the upper cylindrical part60 is arranged or aligned to engage the upper end 72 of lowercylindrical part 61 to form the cylindrical tank wall structure 53. Inthis manner, the upper surface 75 of the second annular flange portion71 will engage or contact the lower surface 68 of the first flangeportion 64. The upper flange means 56 includes first and second flangeportions 64, 71, respectively, and the lower end 65 of upper part 60.

The tank bottom 54 is shown as being a circular platelike member havinga horizontal lower face arranged in downwardly thusting relation to thefoundation or support 13, a horizontal upper face 81, an integralannular marginal portion 82 extending radially outwardly under the thirdflange portion 73 beyond the outer surface 70 of the lower cylindricalpart 61 and beyond third flange portion 73, and an integrally formedvertical cylindrical portion 83 upstanding from the outermost part ofmarginal portion 82 to be concentrically arranged with lower cylindricalpart 61 and having inner and outer cyclindrical surfaces 84, 85,respectively. The lower end 74 of lower cylindrical part 61 is shownengaging a portion of the bottom such that the lower surface 79 of thirdflange portion-73 engages or contacts an annular portion of the bottomupper face 81.

In the preferred embodiment shown and described, the lower flange means58 includes the third flange portion 73, the bottom marginal portion 82,and the cylindrical portion 83 upstanding therefrom.

The anchorage means 59 broadly includes a plurality of circularly spacedinverted L-shaped angle sections or contact members 86, and acorresponding plurality of bolt means 88 fixed to the support 13 andarranged to act on the upper surface 66 of the upper flange means 56.Each contact member 86 includes a horizontal contact plate 89 having anupper surface 90 arranged to be acted upon by one of the bolt means anda lower surface 91 contacting or slidably engaging the upper surface 66of first flange portion 64 for distributing the downward force exertedby the bolt means over the area of contact between plate lower surface91 and first flange portion upper surface 66, and an integral verticalleg 92 depending from an outermost part of plate 89 and having a lowerend 93 arranged to engage or contact a portion of the support 13.

Each of the bolt means 88 includes an anchor bolt 94 having its lowerhooked end 95 suitably embedded or secured in foundation 13 and havingits vertical threaded end portion 96 extending upwardly through a hole98 provided in plate 89, and a nut 99 arranged on the threaded endportion 96 and rotatable to engage or act on the upper surface 90 of thecontact plate. Each of nuts 99 may be suitably tightened to act directlyon the plate upper surface 90 for exerting a downward force on the uppersurface 66 of the upper flange means 56, which force will be distributedover the area of contact between plate lower surface 91 and the firstflange portion upper surface 66 and which may be represented as having acircularly segmented downwardly acting resultant force (F,) as bestdepicted in FIG. 19.

The annular trough between cylindrical surfaces 70 and 84 and the uppersurface 78 of the third flange portion is filled with a resin-sandmixture 100 in which the lower end of the steel cable is embedded andsecured. The intermediate portion of the cable is helically wound aboutthe outer surface of the cylindrical side wall structure such that thevertical spacing between adjacent cable convolutions 101 increases withheight above the tank bottom.

In FIG. 17, laminated corner battens 102 are shown applied to the innercylindrical surface and bottom of the tank to join and seal the innercylindrical surfaces 62, 69 of the upper and lower cylindrical parts 60,61, respectively, and the annular side wall structure to the bottom.

In the preferred embodiments, an inverted U-shaped plastic stiffeningmember 103 is positioned beneath each angle section 86 to engage theupper surface 78 of the third flange portion and the lower surface 76 ofthe second flange portion to prevent localized buckling of the upperflange means when nut 99 is tightened to exert a downward force thereon.

While the wall structure has been described as including upper and lowercylindrical parts, it should be readily apparent to one skilled in thisart that an improved tank incorporating the inventive resisting meansmay also be provided with a unitary or sectional wall structure.

After the tank 52 has been initially designed to have the requiredcapacity and to accommodate the intended service fluid, the resistingmeans 55 may be designed and suitably dimensioned. Anticipating that aseismic force (F,,) or a wind force may be applied to the tank from anydirection, the resisting means is designed by considering that a leadingportion 51 of the wall structure will be placed in tension and that atrailing portion 50 will be placed in compression, and by dimensioningthe resisting means to withstand the greater additional flexure stressattributable to the rotational or torsional moments applied thereto atthe point of maximum compression (FIG. 18) or at the point of maximumtension (FIG. 19).

Referring to FIG. 18, the seismic flexure stress (1;) is assumed to beevenly distributed across the thin radial thickness (t) of the trailingportion 50 of the side wall structure to produce a maximum downward unitcompressive force (f acting at the center of the wall structure andwhich may be calculated according to the equation:

ft Us) Thereafter, the maximum rotational or torsional moment (M,)applied to the compressive side may be calculated by considering thatthe maximum net downward compressive force (f in the side wall structurewill be opposed by an equal distributed upward force exerted by thefoundation on a portion of the bottom lower face 80 between innersurface 69 and outer surface 85, such opposing force having an upwardresultant force (F applied to bottom lower face 80 approximately midwaybetween surfaces 69 and 85. The maximum torsional or rotational momentin the compression side (M may be calculated by considering that thedownward compressive force (f will act at an arm distance (X,) from thepoint of application of the upward resultant force (F to exert aclockwise moment (M on the resisting means. Accordingly,

e (fr) 0 Thereafter, the upper and lower flange means 56, 58,respectively, may be suitably spaced and dimensioned to locate thecentroid (Z) of the polar moment of inertia (I,,) of the upper and lowerflange means and the wall structure therebetween approximatelyequidistant from each of the furthermost fibers thereof, namely, pointsA and B on the upper flange means and points C and D of the lower flangemeans.

The maximum flexure stress on the compression side (M at each ofrpointsA, B, C and D may be calculated according to the equation:

where: R,, is the radius to the centroid, and C is the distance from thecentroid to the furthest point of the upper and lower flange means(point A, B, C or D).

Referring to FIG. 19, the seismic flexure stress (fl,) is similarlyassumed to be evenly distributed across the radial thickness (z) of theleading portion of the wall structure to produce a maximum unit tensileforce (f acting upwardly at the center of the wall structure and whichmay be calculatedaccording to the equation:

fi 0%) (t) On the tension side, the maximum upward tensile force (f inthe leading portion 51 will be resisted by an opposite downward forceexerted by the anchorage means acting across the area of contact betweenupper surface 66 and plate lower surface 91, such force beingrepresented as having a downward resultant (F acting at the center ofsuch area of contact and spaced from the upward tensile force ()1) by anarm distance (X Hence, the magnitude of the rotational moment (M,) onthe tension side may be calculated according to the equation: I

The maximum flexure stress (s,) on the tension side at each offurthermost points A, B, C and D may also be calculated according to theequation:

In the schematic illustrations of FIGS. 18 and 19, the effective momentarm on the tension side (x,) is greater than the corresponding momentarm (x on the compression side. Hence, the maximum torsional moment onthe tensile side (M willbe greater than the maximum torsional moment onthe compression side (M Accordingly, the maximum flexure stress on thetension side (s,) at points A, B, C and D will be greater than on thecompression side (s and this greater value should be employed in thedesign of the anchorage means.

The radius (R,,) of the anchor bolt circle may then be selected and theunit load (f thereon computed according to the equation:

90 at a distance (a) from the center of leg 92. Hence. the maximumupward pull (F,,) on the bolts may be calculated by considering themoments about the center of leg 92. Accordingly,

F, (L) Pb a a Thereafter, the minimum number, size and spacing of thebolt means may be calculated.

For the convenience of those skilled in the art, but not to be construedas a limitation on the claims appended hereto, the vertical thickness ofthe first, second, and third flange portions, 64, 71 and 82,respectively; the vertical thickness of the bottom marginal portion 82;and the radial thickness of cylindrical portion 83 may severally bedimensioned to be equal to the radial thickness (t) of the side wallstructure. While this configuration is arbitrary, it serves to reduceand lower number of variables in dimensioning and spacing the upperandlower flange means to position the centroid (Z) of its cross-sectionequidistant from furthermost points A, B, C and D.

While preferred embodiments of the invention have been shown anddescribed, it should be clearly understood by a person having ordinaryskill in this art that various changes and modifications may be madewithout departing from the spirit of the invention which is defined bythe following claims.

What is claimed is: 1. An upstanding fiberglass reinforced plastic tankadapted to receive and store a fluid exposed to atmospheric pressure,said tank having a bottom resting on a support and having a cylindricalside wall structure, the head ofa fluid within said tank exertinghydrostatic pressure on said side wall structure which urges said sidewall structure to expand in a radial direction, wherein the improvementcomprises:

resisting means arranged at the lower portion of said tank and adaptedto resist torsional stress in said tank lower portion produced by anexternal overturning moment applied to said tank, said moment causing astress reversal in said tank lower portion by producing tensile forcesin one part of said side wall structure and compressive forces inanother part thereof, said resisting means including annular lowerflange means extending radially outwardly from said tank and having alower face arranged in downwardly thrusting relation to said support;

annular upper flange means extending radially outwardly from said tankand arranged in vertically spaced relation to said lower flange means;and

anchorage means secured to said support and arranged to slidably engagesaid upper flange means and adapted to exert substantial downward forcethereon when said moment is applied tosaid tank,

whereby such sliding engagement between said anchorage means and upperflange means may permit radial expansion of said side wall structureand, when said moment is applied to said tank, the tensile forces insaid one tank part may be resisted by downward force exerted on saidupper flange means by said anchorage means, and the compressive forcesin such other tank part may be resisted by an upward force exerted bysaid support on said lower flange means.

2. The improvement as set forth in claim 1 wherein said side wallstructure includes an upper cylindrical part having a first annularflange portion extending radially outwardly from a lower end thereof,and includes a lower cylindrical part having a second annular flangeportion extending radially outwardly from an upper end thereof and athird annular flange portion extending radially outwardly from a lowerend thereof, said lower end of said upper cylindrical part being adaptedto rest on said upper end of said lower cylindrical part such that saidfirst and second flange portions form said upper flange means, and saidlower end of said lower cylindrical part being adapted to rest on anannular marginal portion of said bottom extending beneath said thirdflange portion such that said third flange portion and said bottommarginal portion form said lower flange means.

3. The improvement as set forth in claim 1 wherein said anchorage meanscomprises a contact member having a leg portion arranged to engage saidsupport and a plate portion adapted to engage said upper flange means,and bolt means secured to said support and adapted to act against saidplate portion such that, when said moment is applied to said tank, saidplate portion may exert said downward force on said upper flange meansto resist said tensile forces.

4. The improvement as set forth in claim 1 wherein said lower flangemeans further includes a cylindrical portion upstanding from an outerpart thereof and arranged in spaced concentric relation to said sidewall structure.

1. An upstanding fiberglass reinforced plastic tank adapted to receiveand store a fluid exposed to atmospheric pressure, said tank having abottom resting on a support and having a cylindrical side wallstructure, the head of a fluid within said tank exerting hydrostaticpressure on said side wall structure which urges said side wallstructure to expand in a radial direction, wherein the improvementcomprises: resisting means arranged at the lower portion of said tankand adapted to resist torsional stress in said tank lower portionproduced by an external overturning moment applied to said tank, saidmoment causing a stress reversal in said tank lower portion by producingtensile forces in one part of said side wall structure and compressiveforces in another part thereof, said resisting means including annularlower flange means extending radially outwardly from said tank andhaving a lower face arranged in downwardly thrusting relation to saidsupport; annular upper flange means extending radially outwardly fromsaid tank and arranged in vertically spaced relation to said lowerflange means; and anchorage means secured to said support and arrangedto slidably engage said upper flange means and adapted to exertsubstantial downward force thereon when said moment is applied to saidtank, whereby such sliding engagement between said anchorage means andupper flange means may permit radial expansion of said side wallstructure and, when said moment is applied to said tank, the tensileforces in said one tank part may be resisted by downward force exertedon said upper flange means by said anchorage means, and the compressiveforces in such other tank part may be resisted by an upward forceexerted by said support on said lower flange means.
 2. The improvementas set forth in claim 1 wherein said side wall structure includes anupper cylindrical part having a first annular flange portion extendingradially outwardly from a lower end thereof, and includes a lowercylindrical part having a second annular flange portion extendingradially outwardly from an upper end thereof and a third annular flangeportion extending radially outwardly from a lower end thereof, saidlower end of said upper cylindrical part being adApted to rest on saidupper end of said lower cylindrical part such that said first and secondflange portions form said upper flange means, and said lower end of saidlower cylindrical part being adapted to rest on an annular marginalportion of said bottom extending beneath said third flange portion suchthat said third flange portion and said bottom marginal portion formsaid lower flange means.
 3. The improvement as set forth in claim 1wherein said anchorage means comprises a contact member having a legportion arranged to engage said support and a plate portion adapted toengage said upper flange means, and bolt means secured to said supportand adapted to act against said plate portion such that, when saidmoment is applied to said tank, said plate portion may exert saiddownward force on said upper flange means to resist said tensile forces.4. The improvement as set forth in claim 1 wherein said lower flangemeans further includes a cylindrical portion upstanding from an outerpart thereof and arranged in spaced concentric relation to said sidewall structure.